A molding is generally provided with date of manufacture, lot number, product number, etc. on its surface and these indications are used for investigating, the causes leading to defects in the molding and for performing inventory control. An indication body comprising a marking indication part is attachably and detachably inserted into inner surface of a molding mold and then the molding is molded with the indication body inserted therein. As a result, these indications, including the marking contents of the indication body in its entirety, are marked and molded on the surface of the molding.
Japanese Patent Publication No. 3470880 discloses a marking device comprising such an indication body. The marking device disclosed by the Patent Publication No. 3470880 is shown in FIG. 10.
As shown in FIG. 10, the marking device disclosed by the Patent Publication No. 3470880 consists of a substantially cylindrical outer shell body (O) on which surface indications are marked, a substantially bolt-shaped index body (I), a spring (S), a nut (N), and a cover body (C).
The index body (I) is fit into the outer shell (O) from upper side of the outer shell (O). The nut (N) is placed from lower side to the inside of the outer shell body (O) and is threadedly engaged with a threaded part (I1) formed in a lower part of the index both (I). The spring (S) is arranged between the nut (N) and a projecting step part (O1) formed at intermediate position in an axial direction of the inner wall of the outer shell body (O), and downwardly biases the nut (N) with the force and the index body (I) connected with the nut (N). The cover body (C) is threadedly engaged with female thread parts formed in the lower part of the inner wall of the outer shell body (O), and blocks a lower opening of the outer shell body (O).
At the intermediate position of the index body (I), the projecting part (I2) consisting of a spring and a sphere projects in a radial direction of the index body (I). Moreover, the projecting step part (O1) of the outer shell body (O) has a plurality of positioning grooves (O3) formed continuously and at equal intervals in a circumferential direction, into which the projecting part (I2) is fit.
The marking device disclosed by the Patent Publication No. 3470880 has a structure such that if the index body (I) rotates, the projecting part (I2) projecting from the index body (I) is fit into the positioning grooves (O3), leading to secure fixation of angular positions of the index body at a desired position.
According to the marking device disclosed by the Patent Publication No. 3470880, when the nut (N) is threadedly engaged with the threaded part (I1) of the index body (I), an engaging projection (N1) formed on outer surface of the nut (N) and the outer shell body (O) engage each other. This engagement prevents the nut (N) from rotating when the index body (I) rotates, and the nut (N) moves only in upper direction of the axis of the outer shell body (O). If the index body (I) repeatedly keeps rotating in accordance with the use of the marking device, however, the nut (N) comes into contact with the projecting step part (O1) and is then locked, which prevents the nut (N) from moving in upper direction of the outer shell body (O) axis. As a result, the index body (I) can no longer rotate. In order to rotates the index body (I) again, it is necessary to move the nut (N) to the lower part of the threaded part (I1). Therefore, it was required to remove the marking device from the mold once, remove the index body (I) from the marking device, move the nut (N) to the lower part of the index body (I), mount the index body (I) to the marking device, and then mount the marking device to the mold. Furthermore, molding of a resin by heating and melting the resin may produce gas from the melted resin. In a conventional marking device, the gas produced from the melted resin enters the inside of the marking device through the space between the upper part (index part) of the index body and the inner wall surface of the outer shell body (O), and solidifies in the gap between the threaded part (I1) of the index body and the nut (N). This can prevent the index body (I) from rotating. In such a case, it was necessary to remove the solidified product (residue) by using a solvent etc., which was troublesome.
Furthermore, in order to remove the marking device from the mold for maintenance, the marking, device is removed by being hit with a hammer etc. through a hole provided to face a surface opposite from the surface the marking device is attached on. However, it may be difficult to hit with a hammer etc. and remove the marking device due to positional relationship of pipes such as a cooling path provided in the mold. In this case, a stick etc. is welded, on top surface of the index body 1 and pulled, so that the marking, device is pulled out of and removed from the mold. This detaching work is troublesome and time-consuming, and therefore, the maintenance work was inefficient.